A growing need exists to measure the total content of organic carbons (OC) in public waters, such as river water, etc., or in industrial waste waters. A conventional method of measuring the content of total organic carbons (TOC) in a water sample is as follows. First, the sample is pre-processed to eliminate inorganic carbons (IC). That is, an inorganic acid, such as hydrochloric acid or sulfuric acid, is added to the sample, and, as shown in FIG. 1A, a high purity air from an air cylinder 11 is blown into the sample 10 to convert the inorganic carbons to CO.sub.2 and purge the CO.sub.2 out of the sample 10.
After the pre-processing, the sample 10 is sent to a TC combustion tube 15, where the sample 10 is heated to a high temperature (i.e., combusted) and all of the carbon included in the sample 10 is converted to CO.sub.2. The combustion gas is sent to a non-dispersive infrared gas analyzer (NDIR) 21 in (FIG. 1B,) where the amount of CO.sub.2 in the gas is measured. The controller 22 of the total organic carbons analyzer calculates the TOC content of the sample 10 from the amount of CO.sub.2 measured by the NDIR 21 and the amount of sample 10 sent to the TC combustion tube 15.
There is a problem in pre-processing sample 10 to purge out the inorganic carbons. When the high purity air is blown into the sample 10, purgeable organic carbons (POC) are also purged out of the sample 10. Thus, in the above method, the content of purgeable organic carbons must be measured separately to measure the correct total organic carbons content. In order to measure the POC content, a purgeable organic carbons analyzer 17 is incorporated in the TOC analyzer, as shown in FIG. 1A.
The operation of a POC analyzer can be understood referring to FIG. 2. First, the same amount of sample 10 as sent to the TC combustion tube 15 in the above measurement is sent to a purger 27. Then high purity air is passed through the sample 10 by injecting the gas in the bottom of purger 27. The amount of high purity air injected into the purger 27 is the same as that blown into the sample 10 in the above described pre-processing step, whereby the same amount of purgeable organic carbons as purged from the sample 10 in the pre-processing is purged out from the sample 10 in the purger 27. The purgeable organic carbons content of the sample 10 can then be obtained by sending the gas from the purger 27 to the TC combustion tube 15 in the TOC analyzer.
There is another problem in the above method. Because part of the inorganic carbons (IC) is purged out of sample 10 as CO.sub.2 when the high purity air is injected into the sample 10 in purger 27 as, it is necessary to eliminate CO.sub.2 before the gas from the purger 27 is sent to the TC combustion tube 15 in order to measure the correct content of purgeable organic carbons. Thus a CO.sub.2 absorber 28 is provided in the POC analyzer 17, as shown in FIG. 2.